AITAH for refusing to switch wedding dates after my brother got engaged?

My fiancé and I decided our wedding date over a year ago. Everything is planned, deposits paid. My brother just got engaged and now wants my exact date because it’s “meaningful” to him and his fiancée.

I thought he was joking, but he was dead serious. He asked if we could move ours since we booked first and had “more flexibility.” I told him absolutely not. Now he’s pissed, our parents are saying I should be the bigger person, and his fiancée is acting like I ruined her dream.

I don’t get it. why should I upend everything for them? AITAH?